9905-976

About the 9905-976

Three separate speed calculations are performed and put to a two-out-of-three hardware vote to determine whether overspeed conditions have been met. If an overspeed condition is detected by only one of the three speed-sensing units, only that unit will trip. If the condition is detected by two of the three units, a trip relay is activated for the entire 9905-976 system. This is an energize-to-trip model in the Woodward ProTech 203 series.

All three units are interfaced with a magnetic pickup (MPU) to monitor prime mover speed. From speed sampling (done every 5 ms) to the activation of a trip relay, the ProTech 203 9905-976 overspeed protection system has an overall response time of 40 ms max. Coupled with the modular design and voting configuration of this device, the 9905-976 system minimizes prime mover downtime.

Units A, B, and C in model 9905-976 are identical. They each have a 120 Vac/dc power supply and an operator interface.  Although these units are programmed separately, they need to have identical parameters set for the overall system to function correctly.  

A few of the tunable parameters include:

• Trip speed set point (250 rpm minimum, 25,000 rpm maximum)
• MPU fail set point (100 rpm minimum, 25,000 rpm maximum)
• Trip on MPU failure

A full list of tunable parameters for the 9905-976 model is in Woodward ProTech 203 manual 85195. This manual also contains additional device specifications and programming information.